1. Field of the Invention
This invention concerns treatment of waste anesthetic gases from healthcare or other facilities that use inhaled anesthetics for medical or veterinary purposes. In particular, the invention pertains to the removal and reclamation of nitrous oxide, flouroethers, and other halocarbons from a stream of waste anesthetic gases produced by one or more anesthesia delivery systems of a healthcare facility in order to reduce atmospheric pollution before the gas stream is discharged to the atmosphere.
2. Description of the Prior Art
Anesthesia delivery systems in surgical facilities (both hospital and outpatient) produce significant quantities of waste anesthetic gases. Currently these gases are collected from the patients' exhalation by a dedicated or shared vacuum system. The healthcare facilities typically employ one or more centrally-located vacuum pumps to collect waste gases from individual anesthetizing locations. These vacuum pumps are usually oversized, because they are designed to collect exhaled anesthetics over a wide range of flows. Because these pumps operate continuously, the waste anesthetic gas suction system also entrains large amounts of surrounding room air from the anesthetizing locations, significantly diluting the waste anesthetic gases therein. At the central vacuum pump(s), the gas stream is often admixed with additional room air to further dilute it prior to its ejection from the facility. This dilute waste anesthetic gas/air mixture is typically pumped to the outside of the medical facility, where it is vented to the atmosphere.
The waste anesthetic gases are generally collected at about 20-30° C. with relative humidity ranging between 10 to 60 percent. The average composition of the waste gases is estimated to be (in percent volume) 25-32 percent oxygen, 60-65 percent nitrogen, 5-10 percent nitrous oxide, and 0.1-0.5 percent volatile halocarbons, including flouroethers such as isoflurane, desflurane and sevoflurane. The waste anesthetic gas may also contain trace lubricating oil vapor from vacuum pumps. Like Freon-12® and similar refrigerants, waste anesthetic gas halocarbons (primarily halogenated ethers) contribute to ozone depletion and environmental warming, and they represent an increasingly significant source of environmental concern. Although waste anesthetic gas emissions have thus far escaped environmental regulation in the United States, it is likely that legislative initiatives for ultimate strict regulation of waste anesthetic gas emissions will occur in the near future.
Several techniques have been proposed to treat waste anesthetic gases in an attempt to remedy the growing problem of waste anesthetic gas emissions. For example, U.S. Pat. No. 4,259,303 describes the treatment of laughing gas with a catalyst, U.S. Pat. No. 5,044,363 describes the adsorption of anesthetic gases by charcoal granules, U.S. Pat. No. 5,759,504 details the destruction of anesthetic gases by heating in the presence of a catalyst, U.S. Pat. No. 5,928,411 discloses absorption of anesthetic gases by a molecular sieve, and U.S. Pat. No. 6,134,914 describes the separation of xenon from exhaled anesthetic gas. A cryogenic method for scrubbing volatile halocarbons from waste anesthetic gas is taught by Berry in U.S. Pat. No. 6,729,329, which is incorporated herein by reference.
FIG. 1 illustrates a typical waste anesthetic gas reclamation system (10) of prior art for a healthcare facility. The system (10) includes a number of individual anesthetizing stations (15A, 15B, 15C), each having an anesthetizing machine (12A, 12B, 12C) which delivers anesthesia to a patient via a mask (14A, 14B, 14C) or similar device. Excess anesthetic gases, patients' exhalation, and air are collected at the masks (14A, 14B, 14C) by the anesthetizing machines (12A, 12B, 12C) and discharged to a common collection manifold (16). The waste anesthetic gas collection manifold is typically hard plumbed into the healthcare facility, and the anesthetizing machines (12A, 12B, 12C) are removably connected to the collection manifold (16) at standard waste anesthetic gas connectors (18A, 18B, 18C), e.g. 19 mm or 30 mm anesthetic connectors. The waste anesthetic gas collection system (10) operates at a vacuum pressure which is generated by one or more central vacuum pumps (20). The collected waste gas stream is typically passed through one or more heat exchanger condensers (22). A source of liquid oxygen, or other suitable heat sink, extracts heat from the waste anesthetic stream, condensing the anesthetic gas components. The liquid waste anesthetic condensate is captured in a collection vessel (24). The remaining gas stream, stripped of waste anesthetic gas components, passes through a receiver (26) and the vacuum pump(s) (20), and it is then exhausted to the atmosphere outside of the healthcare facility.
The current methods for scavenging waste anesthetic gases from anesthetizing locations (15A, 15B, 15C) in healthcare facilities generally involve drawing high flows of room air into the dedicated or shared vacuum collection manifold (16) to entrain waste anesthetic gases. The collection manifold (16) may also continuously draw in air through a number of idle anesthetizing machines (12A, 12B, 12C). On average, the collection system manifold (16) extracts between 20-30 liters of waste anesthetic gas and/or room air per minute at each anesthetizing location (15A, 15B, 15C). For a large hospital having between 20-30 operating rooms, it is estimated that waste anesthetic reclamation system (10) flow rate ranges between 500-1000 l/min. (14-35 scf/min.).
The advantages of a high-flow dilute waste gas system are that the system easily accommodates a wide range of anesthetic exhaust flows, the system is safe, in that little anesthetic can escape the system, and the system is simple, requiring little maintenance. However, high-flow systems are energy-intensive, generally requiring large vacuum pumps (20) in order to maintain sufficient suction at a large number of anesthetizing stations (15A, 15B, 15C). For example, to maintain a vacuum of about 200 mm Hg at a flow rate of 1-2 cfm at each anesthetizing station (15A, 15B, 15C), vacuum pumps of 100-200 cfm capacity are common. Furthermore, because removal of a waste component by condensation requires lowering the temperature of the flow stream to a point where the partial pressure of the waste component is equal to or greater than its saturated vapor pressure (at that temperature), diluted waste anesthetic gas concentrations can hamper efficient recovery by condensation processes. A method and system for increasing the efficacy and efficiency of condensation-type waste anesthetic gas scavenging and reclamation systems is thus desirable.
3. Identification of Objects of the Invention
A primary object of the invention is to provide an economical system and method for removing flouroethers and other volatile halocarbons from waste anesthetic gases from a surgical or other healthcare facility before such gases are vented to the atmosphere.
Another object of the invention is to provide an economical system and method for removing nitrous oxide from waste anesthetic gases from a surgical or other healthcare facility before such gases are vented to the atmosphere.
Another object of the invention is to provide an economical system and method for substantially preventing atmospheric venting of flouroethers and other volatile halocarbons of waste anesthetic gas while eliminating the need of prior art catalysts, charcoal granules and heating techniques.
Another object of the invention is to provide an economical system and method for increasing the efficacy and efficiency of condensation-type waste anesthetic scavenging systems.
Another object of the invention is to provide an economical system and method which utilizes and enhances existing waste anesthetic gas reclamation systems of healthcare facilities for minimal impact and cost.
Another object of the invention is to provide a system and method which requires minimal additional investment for a healthcare facility to implement.
Another object of the invention is to provide a system and method which reclaims and allows re-distillation and/or reuse of a large percentage of the nitrous oxide and/or anesthetic halocarbon used in the facility.
Another object of the invention is to provide a system and method which reduces anesthetic-related halocarbon emissions from a healthcare facility into the atmosphere by about 99 percent or more.